Alkali-free aluminoborosilicate glass, and uses thereof

ABSTRACT

An alkali-free aluminoborosilicate glass having a coefficient of thermal expansion α 20/300  of between 2.8×10 −6 /K and 3.8×10 −6 /K, which has the following composition (in % by weight, based on oxide): silicon dioxide (SiO 2 )&gt;58−65, boric oxide (B 2 O 3 )&gt;6−11.5, magnesium oxide (MgO) 4−8, barium oxide (BaO) 0−&lt;0.5, zinc oxide (ZnO) 0−2 and aluminum oxide (Al 2 O 3 )&gt;14−25, calcium oxide (CaO) 0−8, strontium oxide (SrO) 2.6−&lt;4, with barium oxide (BaO)+strontium oxide (SrO) &gt;3, or aluminum oxide (Al 2 O 3 )&gt;14−25, calcium oxide (CaO) 0−&lt;2, strontium oxide (SrO)&gt;0.5−&lt;4, or aluminum oxide (Al 2 O 3 )&gt;21−25, calcium oxide (CaO) 0−8, strontium oxide (SrO)&gt;2.6−&lt;8, with barium oxide (BaO)−strontium oxide (SrO)&gt;3, and which is highly suitable for use as a substrate glass both in display technology and in thin-film photovoltaics.

[0001] CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0002] This application is related to U.S. application Ser. No.______ ,filed concurrently herewith on Jan. 11, 2001, having the titleALKALI-FREE ALUMINOBOROSILICATE GLASS, AND USES THEREOF, naming asinventors Dr. Ulrich PEUCHERT and Dr. Peter BRIX, and identified byAttorney Docket No. NHL-SCT-18.

[0003] This application is also related to U.S. application Ser.No.______ , filed concurrently herewith on Jan. 11, 2001, having thetitle ALKALI-FREE ALUMINOBOROSILICATE GLASS, AND USES THEREOF, naming asinventors Dr. Ulrich PEUCHERT and Dr. Peter BRIX, and identified byAttorney Docket No. NHL-SCT-19.

[0004] This application is further related to U.S. application Ser.No.______ , filed concurrently herewith on Jan. 11, 2001, having thetitle ALKALI-FREE ALUMINOBOROSILICATE GLASS, AND USES THEREOF, naming asinventors Dr. Ulrich PEUCHERT and Dr. Peter BRIX, and identified byAttorney Docket No. NHL-SCT-20.

BACKGROUND OF THE INVENTION

[0005] 1. Field of the Invention

[0006] The invention relates to alkali-free aluminoborosilicate glasses.The invention also relates to uses of these glasses.

[0007] 2. Background of the Invention

[0008] High requirements are made of glasses for applications assubstrates in flat-panel liquid-crystal (or expressed differently:liquid crystal) display technology, for example in TN (twistednematic)/STN (supertwisted nematic, or expressed differently: supertwisted nematic) displays, active matrix liquid crystal displays(AMLCDs), thin-film transistors (TFTs) or plasma addressed liquidcrystals (PALCs). Besides high thermal shock resistance and goodresistance to the aggressive chemicals employed in the process for theproduction of flat-panel screens, the glasses should have hightransparency over a broad spectral range (VIS, UV) and, in order to saveweight, a low density. Use as substrate material for integratedsemiconductor circuits, for example in TFT displays (“chip on glass”) inaddition requires thermal matching to the thin-film material siliconwhich is usually deposited on the glass substrate in the form ofamorphous silicon (a-Si) at low temperatures of up to 300° C. Theamorphous silicon is partially recrystallized by subsequent heattreatment at temperatures of about 600° C. Owing to the a-Si fractions,the resulting, partially crystalline poly-Si layer is characterized by athermal expansion coefficient of α_(20/300) ≅3.7×10⁻⁶/K. Depending onthe a-Si/poly-Si ratio, the thermal expansion coefficient α_(20/300) mayvary between 2.9×10^(−6/)K and 4.2×10⁻⁶/K. When substantiallycrystalline Si layers are generated by high temperature treatments above700° C. or direct deposition by CVD processes, which is likewise desiredin thin-film photovoltaics, a substrate is required which has asignificantly reduced thermal expansion of 3.2×10⁻⁶/K or less.

[0009] In addition, applications in display and photovoltaics technologyrequire the absence of alkali metal ions. Sodium oxide levels of lessthan 1000 ppm (parts per million) as a result of production can betolerated in view of the generally “poisoning” action due to diffusionof Na⁺ into the semiconductor layer.

[0010] It should be possible to produce suitable glasses economically ona large industrial scale in adequate quality (no bubbles, knots,inclusions), for example in a float plant or by drawing methods. Inparticular, the production of thin (<1 mm) streak-free substrates withlow surface undulation by drawing methods requires high devitrificationstability of the glasses. Compaction of the substrate during production,in particular in the case of TFT displays, which has a disadvantageouseffect on the semiconductor microstructure, can be countered byestablishing a suitable temperature-dependent viscosity characteristicline of the glass: with respect to thermal process and shape stability,it should have a sufficiently high glass transition temperature T_(g),i.e. T_(g)>700° C., while on the other hand not having excessively highmelting and processing (V_(A)) temperature, i.e. a V_(A) of<1350° C.

[0011] The requirements of glass substrates for LCD display technologyor thin-film photovoltaics technology are also described in “Glasssubstrates for AMLCD applications: properties and implications” by J. C.Lapp, SPIE Proceedings, Vol. 3014, invited paper (1997), and in“Photovoltaik—Strom aus der Sonne” by J. Schmid, Verlag C. F. Müller,Heidelberg 1994, respectively.

[0012] The abovementioned requirement profile is fulfilled best byalkaline earth metal aluminoborosilicate glasses. However, the knowndisplay or solar cell substrate glasses described in the followingpublications still have disadvantages and do not meet the full list ofrequirements:

[0013] Numerous documents describe glasses having low MgO contents: JP9-169 538 A, JP 4-160 030 A, JP 9-100 135 A, EP 714 862 Al, EP 341 313Bl, U.S, Pat. No. 5,374,595, WO 97/11919 and WO 97/11920. Such glasses,in particular those of EP 714 862 Al and JP 9-169538 A, do not have thedesired meltability, as is evident from very high temperatures atviscosities of 10² dPas and 10⁴ dpas, and have a relatively highdensity. The same applies to the Mgo-free glasses of DE 37 30 410 A1.

[0014] The glasses of U.S. Pat. No. 5,374,595 have high BaO contents of2-7 mol % which leads to undesirably high densities of these glasses.The same applies to the glasses of JP 61-132536 A, JP 8-295530 A, JP9-48632 A and JP 9-156953 A.

[0015] Similarly, the glasses of JP 10-72237 A having high SrO contentshave very high temperatures at viscosities of 10² dPas and 10⁴ dpas, asis evident from the examples.

[0016] The same is true for glasses having low B₂O₃ contents asdescribed in JP 9-263421 A and JP 10-45422 A. The devitrificationtendency will be disadvantageously high, in particular in combinationwith low BaO contents. On the other hand, excessively high B₂O₃contents—such glasses are described, for example, in U.S. Pat. No.4,824,808—are disadvantageous for the intended properties of high heatresistance and high chemical resistance, in particular to hydrochloricacid solutions.

[0017] Low-SiO₂ glasses do not have sufficient chemical resistanceeither, in particular when they contain relatively large amounts of B₂O₃and are low in alkaline earth metals. This applies to the glasses of WO97/11919 and EP 672 629 A2. The relatively SiO₂-rich variants of thelatter document have only low Al₂O₃ levels, which is disadvantageous forthe crystallization behavior.

[0018] JP 9-123 33 A, which relates to glasses for hard disks, describescompositions of SiO₂, Al₂O₃, CaO and further optional componentsincluding B₂O₃. The glasses listed have high alkaline earth metal oxidecontents and thus have high thermal expansion, which makes themunsuitable for use in LCD or PV technology. Their visual quality willprobably also be inadequate.

[0019] Federal Republic of Germany Patent No. 196 17 344 C1 (U.S. Pat.No. 5,908,703) and Federal Republic of Germany Patent No. 196 03 698 C1(U.S. Pat. No. 5,770,535) by the Applicant disclose alkali-free, tinoxide-containing, low-SiO₂ or SrO-free glasses having a coefficient ofthermal expansion α_(20/300) of about 3.7·10⁻⁶/K and very good chemicalresistance. They are suitable for use in display technology. However,since they must contain ZnO, they are not ideal, in particular forprocessing in a float plant. In particular at higher ZnO contents (>1.5%by weight), there is a risk of formation of ZnO coatings on the glasssurface by evaporation and subsequent condensation in the hot-shapingrange.

[0020] WO 98/27019 describes glasses for display and photovoltaicsapplications having a low density and a high heat resistance. In theseglasses, some of which have a high CaO content, the SrO and BaO contentsare limited to a total of 3% by weight, which renders the glassessusceptible to crystallization.

[0021] DE 196 01 022 A1 describes glasses which are selected from a verywide composition range and which must contain ZrO₂ and SnO. The glasses,which, according to the examples, have a relatively high BaO content,tend to exhibit glass defects because of the ZrO₂ level which has to bepresent.

[0022] DE 42 13 579 A1 describes glasses for TFT applications having acoefficient of thermal expansion α_(20/300) of <5.5×10⁻⁶/K, according tothe examples of ≧4.0×10⁻⁶/K. These glasses which have relatively highB₂O₃ levels and relatively low SiO₂ contents do not have a high chemicalresistance, in particular to diluted hydrochloric acid.

[0023] In the unexamined Japanese publications JP 10-25132 A, JP10-114538 A, JP 10-130034 A, JP 10-59741 A, JP 10-324526 A, JP 11-43350A, JP 11-49520 A, JP 10-231139 A and JP 10-139467 A, mention is made ofvery wide composition ranges for display glasses, which can be varied bymeans of many optional components and which are admixed with one or morespecific refining agents in each case. However, these documents do notindicate how glasses having the complete requirement profile describedabove can be obtained in a specific manner.

OBJECT OF THE INVENTION

[0024] It is an object of the present invention to provide glasses whichmeet said physical and chemical requirements imposed on glass substratesfor liquid-crystal displays, in particular for TFT displays, and forthin-film solar cells, in particular on the basis of uc-Si, glasseswhich have high heat resistance, a favorable processing range andsufficient devitrification stability.

SUMMARY OF THE INVENTION

[0025] The invention teaches that this object can be achieved byaluminoborosilicate glasses having a coefficient of thermal expansionα_(20/300) of between 2.8×10⁻⁶/K and 3.8×10⁻⁶/K, which has the followingcomposition (in % by weight, based on oxide): silicon dioxide(SiO₂)—from more than 58% to 65% (>58% -65%); boric oxide (B₂O₃)—fromsomewhat more than 6% to 11.5% (>6% -11.5%); aluminum oxide (Al₂O₃)—frommore than 14% to 25% (>14% -25%); magnesium oxide (MgO) from 4% to 8%(4% -8%); calcium oxide (CaO)—from 0% to 8% (0% -8%); strontium oxide(SrO)—from 2.6% to somewhat less than 4% (2.6% -<4%); barium oxide(BaO)—from 0% to somewhat less than 0.5% (0% -<0.5%); with strontiumoxide (SrO)+barium oxide (BaO)—more than 3% (>3%); and zinc oxide(ZnO)—from 0% to 2% (0% -2%).

[0026] The invention also teaches the alkali-free aluminoborosilicateglasses having a coefficient of thermal expansion α_(20/300) of between2.8×10⁻⁶/K and 3.4×10⁻⁶/K, which has the following composition (in % byweight, based on oxide): silicon dioxide (SiO₂)—more than 58% to 65%(>58% -65%); boric oxide (B₂O₃)—from somewhat more than 6% to 11.5% (>6%-11.5%); aluminum oxide (Al₂O₃) from somewhat more than 14% to 25% (>14%-25%); magnesium oxide (MgO)—from 4% to 8% (4% -8%); calcium oxide(CaO)—from 0% to somewhat less than 2% (0% -<2%); strontium oxide(SrO)—from somewhat more than 0.5% to somewhat less than 4% (>0.5%-<4%); barium oxide (BaO)—from 0% to less than 0.5% (0% -<0.5%); andzinc oxide (ZnO)—from 0% to 2% (0% -2%).

[0027] The invention also teaches the alkali-free aluminoborosilicateglasses having a coefficient of thermal expansion α_(20/300) of between2.8×10⁻⁶/K and 3.6×10⁻⁶/K, which has the following composition (in % byweight, based on oxide): silicon dioxide (SiO₂)—from more than 58% to65% (>58% -65%); boric oxide (B₂O₃)—from more than 6% to 11.5% (>6%-11.5%); aluminum oxide (Al₂O₃)—from more than 21% to 25% (>21% -25%);magnesium oxide (Mgo)—from 4% to 8% (4% -8%); calcium oxide (CaO)—from0% to 8% (0% -8%); strontium oxide (SrO)—from 2.6% to somewhat less than8% (2.6% -<8%); barium oxide (BaO)—from 0% to somewhat less than 0.5%(0% -<0.5%); with strontium oxide (SrO)+barium oxide (BaO)—more than 3%(>3%); and zinc oxide (ZnO)—from 0% to 2% (0% -2%).

[0028] The glasses contain from >58 to 65% by weight of SiO₂. At a lowercontent, the chemical resistance is impaired, while at a higher content,the thermal expansion is too low and the crystallization tendency of theglass increases. Preference is given to a content of up to 64.5% byweight of SiO₂.

[0029] The glasses contain from >14 to 25% by weight of Al₂O₃. Al₂O₃ hasa positive effect on the heat resistance of the glasses withoutexcessively increasing the processing temperature. At a lower content,the glasses become more susceptible to crystallization. Preference isgiven to a content of more than 14.5% by weight of Al₂O₃, particularlypreferably more than 18% by weight of Al₂ 0 ₃, most preferably of atleast 20.5% by weight of Al₂O₃, in particular of at least 21% by weightof Al₂O₃. Preference is given to a maximum Al₂O₃ content of 24% byweight.

[0030] The B₂O₃ content is restricted to a maximum of 11.5% by weight inorder to achieve a high glass transition temperature T_(g). Highercontents would also impair the chemical resistance. Preference is givento a maximum B₂O₃ content of 11% by weight. The B₂O₃ content is higherthan 6% by weight to ensure that the glasses have good meltability andgood crystallization stability. Preference is given to a minimum contentof more than 8% by weight.

[0031] The network-forming components Al₂O₃ and B₂O₃ are preferablypresent at mutually dependent minimum levels, ensuring a preferredcontent of the network formers SiO₂, Al₂O₃ and B₂O₃. For example, in thecase of a minimum B₂O₃ content of>6% by weight, the minimum Al₂O₃content is preferably>18% by weight, and in the case of a minimum Al₂O₃content of>14% by weight, the minimum B₂O₃ content is preferably>8% byweight.

[0032] The sum of SiO₂, Al₂O₃ and B₂O₃ is preferably between 83 and 91%by weight.

[0033] An essential glass component are the network-modifying alkalineearth metal oxides. In particular by varying their levels, a coefficientof thermal expansion α_(20/300) of between 2.8×10⁻⁶/K and 3.8×10⁻⁶/K isachieved. The individual oxides are present in the followingproportions:

[0034] The glasses contain from 4 to 8% by weight of MgO. A high MgOlevel has a positive effect on the desired properties of low density andlow processing temperature, whereas a rather low level favorscrystallization stability and chemical resistance.

[0035] The glasses may contain up to 8% by weight of CaO. Higher levelswould lead to an excessive increase in thermal expansion and a decreasein crystallization stability. For glasses exhibiting a particularly lowthermal expansion, i.e. in particular for glasses having coefficients ofthermal expansion α_(20/300) of up to 3.4×10⁻⁶/K, the CaO content ispreferably limited to a maximum of<2% by weight.

[0036] Another optional constituent is BaO, its maximum content beinglimited to less than 0.5% by weight. This ensures good meltability andkeeps the density low. The glass is preferably BaO-free.

[0037] The glass contains up to<4% by weight of the relatively heavyalkaline earth metal oxide SrO. Limitation to this low maximum contentis especially advantageous for a longs density of the glass.

[0038] When the minimum sum of SrO and BaO is more than 3% by weight inorder to ensure sufficient crystallization stability, in particular withrather CaO-rich compositions, the minimum SrO content is 2.6% by weight.

[0039] In the case of low-CaO and CaO-free variants, in particular atCaO contents of between 0 and<2% by weight, a minimum SrO content of atleast>0.5% by weight is sufficient. In the case of these glasses, thesum of SrO and BaO is preferably at least 1% by weight, particularlypreferably at least>1% by weight.

[0040] In the case of high Al₂O₃ contents, i.e. contents of>21% byweight, the SrO content can be varied within wider limits, between 2.6and<8% by weight. As a result of, in particular, the high-SrO contentswhich have now become possible, particularly crystallization-stableglasses having sufficiently low densities are obtained. In the case ofthese glasses, the minimum sum of SrO and BaO is likewise>3% by weight.These glasses have coefficients of thermal expansion α_(20/300) ofbetween 2.8×10⁻⁶/K and 3.6×10⁻⁶/K.

[0041] The glasses may contain up to 2% by weight of ZnO, preferably<2%by weight of ZnO. The network modifier ZnO has a structure-looseningfunction and has less effect on the thermal expansion than the alkalineearth metal oxides. Its effect on the viscosity characteristic line issimilar to that of B₂O₃. In particular in the case of processing of theglasses by the float process, the ZnO level is preferably limited to amaximum of 1.5% by weight. Higher levels would increase the risk ofunwanted ZnO coatings on the glass surface which may form by evaporationand subsequent condensation in the hot-shaping range.

[0042] The glasses are alkali-free. The term “alkali-free” as usedherein means that they are essentially free from alkali metal oxides,although they can contain impurities of less than 1000 ppm (parts permillion).

[0043] The glasses may contain up to 2% by weight of ZrO₂+TiO₂, whereboth the TiO₂ content and the ZrO₂ content can each be up to 2% byweight. ZrO₂ advantageously increases the heat resistance of theglasses. Owing to its low solubility, ZrO₂ does, however, increase therisk of ZrO₂-containing melt relicts, so-called zirconium nests, in theglass. ZrO₂ is therefore preferably omitted. Low ZrO₂ contentsoriginating from corrosion of zirconium-containing trough material areentirely unproblematic. TiO₂ advantageously reduces the solarizationtendency, i.e. the reduction in transmission in the visible wavelengthregion because of UV-VIS radiation. At contents of greater than 2% byweight, color casts can occur due to complex formation with Fe³⁺ ionswhich are present in the glass at low levels as a result of impuritiesof the raw materials employed.

[0044] The glasses may contain conventional refining agents in the usualamounts: they may thus contain up to 1.5% by weight of As₂O₃, Sb₂O₃,SnO₂ and/or CeO₂. It is likewise possible to add 1.5% by weight each ofCl⁻(for example in the form of BaCl₂), F⁻(for example in the form ofCaF₂) or SO₄ ²⁻(for example in the form of BaSO₄) . The sum of As₂O₃,Sb₂O₃, CeO₂, SnO₂, Cl⁻, F⁻ and SO₄ ²⁻ should, however, not exceed 1.5%by weight.

[0045] If the refining agents As₂O₃ and Sb₂O₃ are omitted, these glassescan be processed not only using a variety of drawing methods, but alsoby the float method.

[0046] For example with regard to easy batch preparation, it isadvantageous to be able to omit both ZrO, and SnO₂ and still obtainglasses having the property profile mentioned above, in particularhaving high heat and chemical resistance and low crystallizationtendency.

[0047] The above-discussed embodiments of the present invention will bedescribed further hereinbelow. When the word “invention” is used in thisspecification, the word “invention” includes “inventions”, that is, theplural of “invention”. By stating “invention”, the Applicants do not inany way admit that the present application does not include more thanone patentably and non-obviously distinct invention, and maintains thatthis application may include more than one patentably and non-obviouslydistinct invention. The Applicants hereby assert that the disclosure ofthis application may include more than one invention, and, in the eventthat there is more than one invention, that these inventions may bepatentable and non-obvious one with respect to the other.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0048] The invention is further described with reference to examples,i.e. working examples, as follows.

[0049] Working examples:

[0050] Glasses were produced in Pt/Ir crucibles at 1620° C. fromconventional raw materials which were essentially alkali-free apart fromunavoidable impurities. The melt was refined at this temperature for oneand a half hours, then transferred into inductively heated platinumcrucibles and stirred at 1550° C. for 30 minutes for homogenization.

[0051] The Table shows fourteen examples of glasses according to theinvention with their compositions (in % by weight, based on oxide) andtheir most important properties. The refining agent SnO₂ (Examples 1, 2,4, 5, 7, 8, 10-14) or As₂O₃ (Examples 3, 6, 9) at a level of 0.3% byweight is not listed. The following properties are given:

[0052] the coefficient of thermal expansion α_(20/3000) [10⁻⁶/K]

[0053] the density p [g/cm³]

[0054] the dilatometric glass transition temperature T_(g) [° C.] inaccordance with DIN 52324

[0055] the temperature at a viscosity of 10⁴ dPas (referred to as T 4 [°C.])

[0056] the temperature at a viscosity of 10² dPas (referred to as T 2 [°C.]), calculated from the Vogel-Fulcher-Tammann equation

[0057] the refractive index n_(d).

[0058] the resistance to buffered hydrofluoric acid (“BHF”) as weightloss (material removal value) from glass plates measuring 50 mm×50 mm×2mm and polished on all sides after treatment with 10% strength NH₄F.HFsolution for 20 minutes at 23° C. [mg/cm²]. TABLE Examples: Compositions(in % by weight, based on oxide) and essential properties of glassesaccording to the invention. 1 2 3 4 5 6 7 SiO₂ 58.3 58.3 63.5 62.1 62.163.5 60.8 B₂O₃ 8.5 8.5 9.0 8.2 8.2 9.1 8.2 Al₂O₃ 21.5 21.5 16.5 19.019.0 17.3 16.1 MgO 4.5 6.0 4.5 6.0 7.5 6.0 4.1 CaO 3.4 1.9 3.0 1.5 1.51.8 7.0 SrO 3.5 3.5 3.2 2.0 1.0 2.0 3.5 BaO — — — 0.4 0.4 — — ZnO — — —0.5 — — — α_(20/300) [10⁻⁶/K] 3.26 3.16 3.14 2.96 2.99 2.98 3.76 ρ[g/cm³] 2.48 2.47 2.43 2.45 2.44 n.m. 2.49 T_(g) [° C.] 735 737 723 740729 725 713 T4 [° C.] 1257 1273 1300 1283 1288 1289 1255 T2 [° C.] 16131621 1694 1657 1652 1653 1616 n_(d) 1.522 1.522 1.513 1.516 1.516 1.5201.524 BHF [mg/cm²] 0.71 0.77 0.58 0.65 0.66 0.60 0.60 8 9 10 11 12 13 14SiO₂ 59.5 60.0 60.0 52.5 60.0 60.0 62.6 B₂O₃ 7.5 7.5 6.6 7.5 7.5 10.08.2 Al₂O₃ 21.5 21.5 22.5 18.5 18.5 16.0 14.5 MgO 4.5 4.1 6.0 4.5 5.6 4.24.2 CaO 0.4 3.5 1.1 3.2 4.2 6.0 6.7 SrO 6.0 2.7 3.5 3.5 3.9 3.5 3.5 BaO0.3 0.4 — — — — — ZnO — — — — — — — α_(20/300) [10⁻⁶/K] 3.04 3.12 3.003.19 3.55 3.64 6.72 ρ [g/cm³] 2.49 2.47 2.48 2.46 2.40 2.47 2.47 T_(g)[° C.] 742 746 753 730 730 700 705 T4 [° C.] 1287 1284 1286 1294 12531234 1252 T2 [° C.] 1654 1644 1641 1674 1615 1604 1627 n_(d) 1.518 1.5201.521 1.522 1.524 1.521 1.520 BHF [mg/cm²] 0.81 0.66 0.75 n.m. n.m. n.m.0.58

[0059] Furthermore, acid resistance was determined for the glasses ofexamples 3 and 14, i.e. the “HCl” acid resistance as weight loss(material removal value) from glass plates measuring 50 mm×50 mm×2 mmand polished on all sides after treatment with 5% strength hydrochloricacid for 24 hours at 95° C.: it was found to be 0.78 mg/cm² (glass no.3) and 0.50 mg/cm² (glass no. 14), respectively.

[0060] As the working examples illustrate, the glasses according to theinvention have the following advantageous properties:

[0061] a thermal expansion (α_(20/300) of between 2.8×10⁻⁶/K and3.8×10⁻⁶/K, or between 2.8×10⁻⁶/K and 3.6×10⁻⁶/K, or up to 3.4×10⁻⁶/K,respectively, thus matched to the expansion behavior of both amorphoussilicon and increasingly polycrystalline silicon.

[0062] Tg>700° C., a very high glass transition temperature, i.e. a highheat resistance. This is essential for the lowest possible compaction asa result of production and for use of the glasses as substrates forcoatings with amorphous Si layers and their subsequent annealing.

[0063] p<2.600 g/cm³, a low density.

[0064] a temperature at a viscosity of 10⁴ dPas of at most 1350° C., anda temperature at a viscosity of 10² dPas of at most 1720° C., whichmeans a suitable viscosity characteristic line with regard tohot-shaping and meltability. The glasses can be produced as flat glassesby the various drawing methods, for example microsheet down-draw,up-draw or overflow fusion methods, and, in a preferred embodiment, ifthey are free from As₂O₃ and Sb₂O₃, also by the float process.

[0065] a high chemical resistance, as is evident from good resistance tobuffered hydrofluoric acid solution, which makes them sufficiently inertto the chemicals used in the production of flat-panel screens.

[0066] n_(d)<1.526, a low refractive index. This property is thephysical prerequisite for a high transmission. The glasses have highthermal shock resistance and good devitrification stability.

[0067] The glasses are thus highly suitable for use as substrate glassin display technology, in particular for TFT displays, and in thin-filmphotovoltaics.

[0068] Alkali-free aluminoborosilicate glass in accordance with thepresent invention may, for example, have any value of coefficient ofthermal expansion α_(20/300) in the range of between about 2.8×10⁻⁶/Kand about 3.8×10⁻⁶/K, for example, 2.9×10⁻⁶/K and 3.7×10⁻⁶/K. Thus, thevalue of the coefficient of thermal expansion α_(20/300) is not limitedto the first and final values of the range, but can comprise any valueof coefficient of thermal expansion α_(20/300) between them.

[0069] The alkali-free aluminoborosilicate glasses in accordance withthe present invention may, for example, have any value (in % by weight,based on oxide) of SiO₂ (silica, silicon dioxide) in the range of fromabout 58 to about 65, for example, 59 and 64. Thus, the value for SiO₂,in % by weight, based on oxide, is not limited to the first and finalvalues of the range, but can comprise any value of SiO₂ between them.

[0070] The alkali-free aluminoborosilicate glasses in accordance withthe present invention may, for example, have any value (in % by weight,based on oxide) of B₂O₃ (boric oxide) in the range of from about 6 toabout 11.5, for example, 6.5 and 10. Thus, the value for B₂O₃, in % byweight, based on oxide, is not limited to the first and final values ofthe range, but can comprise any value of B₂O₃ between them.

[0071] Similarly, the alkali-free aluminoborosilicate glass inaccordance with the present invention may, for example, have any value(in % by weight, based on oxide) of Al₂O₃ (alumina, aluminum oxide) inthe range of from about 14 to about 25, for example, 15 and 24. Thus,the value for Al₂O₃, in % by weight, based on oxide, is not limited tothe first and final values of the range, but can comprise any value ofAl₂O₃ between them.

[0072] Thus, components of the composition of the alkali-freealuminoborosilicate glass in accordance with our invention are likewisenot limited to the first and final values of the indicated range, butcan comprise any value between them.

[0073] The expression “coefficient of thermal expansion α_(20/300”) mayindicate the fractional change in the length or volume of a body perdegree of temperature change for the range of from 20 to 300 degreesCelsius.

[0074] The expression uc-Si is to mean in at least one embodiment of theinvention: micro-crystalline silicon.

[0075] The expression thermal expansion coefficient or coefficient ofthermal expansion (α_(20/300)) in at least one embodiment of theinvention is to mean: a nominal thermal coefficient (α) as possiblyapplicable in the temperature range of from 20 to 300 in the Celsiusscale, as possibly applicable in the context of the indicated data.

[0076] The expression glass transition temperature (T_(g)) in at leastone embodiment of the invention is to mean: (1) the temperature belowwhich a substance becomes superconducting; or (2) the temperature atwhich one polymorph changes into the next thermodynamically stablestate; as the shown technical data suggest.

[0077] The density (p) is to mean in at least one embodiment of theinvention: (1) the mass of a substance per unit of volume, expressed askilograms per cubic meter, or expressed in smaller units, grams percubic centimeter; or (2) the degree of opacity of a translucentmaterial; as the technical data suggest.

[0078] The term DIN refers to the German Standard Organization“Deutsches Institute für Normung e.V., in Berlin, Germany, from whichthe numbered standards may be obtained.

[0079] The Vogel-Fulcher-Tammann equation is possibly related to theFulcher equation meaning empirical in derivation; it relates glassviscosity to temperature: loge=−A+B/T−T₀ where the temperature T is indegrees Celsius, A, B, and T₀ are material-specific constants.

[0080] The features disclosed in the various publications, disclosed orincorporated by reference herein, may be used in the embodiments of thepresent invention, as well as, equivalents thereof.

[0081] One feature of the invention resides broadly in the alkali-freealuminoborosilicate glass having a coefficient of thermal expansionα_(20/300) of between 2.8×10⁻⁶/K and 3.8×10⁻⁶/K, which has the followingcomposition (in % by weighs; based on oxide): SiO₂>58-65; B₂O₃>6-11.5;Al₂O₃>14-25; MgO 4-8; CaO 0-8; SrO 2.6-<4; BaO 0-<0.5 with SrO+BaO>3;ZnO 0-2.

[0082] Another feature of the invention resides broadly in thealkali-free aluminoborosilicate glass having a coefficient of thermalexpansion α_(20/300) of between 2.8×10⁻⁶/K and 3.4×10⁻⁶/K, which has thefollowing composition (in % by weight, based on oxide): SiO₂>58-65;B₂O₃>6-11.5; Al₂O₃>14-25; MgO 4-8; CaO 0-<2; SrO>0.5-<4; BaO O<0.5; andZnO 0-2.

[0083] Yet another feature of the invention resides broadly in thealkali-free aluminoborosilicate glass having a coefficient of thermalexpansion α_(20/300) of between 2.8×10⁻⁶/K and 3.6×10⁻⁶/K, which has thefollowing composition (in % by weight, based on oxide): SiO₂>58-65;B₂O₃>6-11.5; Al₂O₃>21-25; MgO 4-8; CaO 0-8; SrO 2.6-<8; BaO 0-<0.5; withSrO+BaO>3; and ZnO 0-2.

[0084] Still another feature of the invention resides broadly in thealuminoborosilicate glass characterized in that it comprises more than18% by weight, preferably at least 20.5% by weight, particularlypreferably at least 21% by weight, of Al₂O₃.

[0085] A further feature of the invention resides broadly in thealuminoborosilicate glass characterized in that the glass comprises morethan 8% by weight of B₂O₃.

[0086] Another feature of the invention resides broadly in thealuminoborosilicate glass characterized in that it additionallycomprises: ZrO₂0-2; TiO₂0-2; with ZrO₂+TiO₂0-2; As₂O₃0-1.5; Sb₂O₃0-1.5;SnO₂0-1.5; CeO₂0-1.; Cl⁻0-1.5; F⁻0-1.5; SO₄ ²⁻0-1.5; withAS₂O₃+Sb₂O₃+SnO₂+CeO₂+Cl⁻+F⁻+SO₄ ²⁻0-1.5.

[0087] Yet another feature of the invention resides broadly in thealuminoborosilicate glass characterized in that the glass is free ofarsenic oxide and antimony oxide, apart from unavoidable impurities, andthat it can be produced in a float plant.

[0088] Still another feature of the invention resides broadly in thealuminoborosilicate glass which has a coefficient of thermal expansionα_(20/300) of between 2.8×10⁻⁶/K and 3.6×10⁻⁶/K, a glass transitiontemperature T_(g) of>700° C. and a density p of<2.600 g/cm³.

[0089] A further feature of the invention resides broadly in the use ofthe aluminoborosilicate glass as substrate glass in display technology.

[0090] Another feature of the invention resides broadly in the use ofthe aluminoborosilicate glass as substrate glass in thin-filmphotovoltaics.

[0091] All, or substantially all, of the components and methods of thevarious embodiments may be used with at least one embodiment or all ofthe embodiments, if more than one embodiment is described herein.

[0092] All of the patents, patent applications and publications recitedherein, and in the Declaration attached hereto, are hereby incorporatedby reference as if set forth in their entirety herein.

[0093] The corresponding foreign and international patent publicationapplications, namely, Federal Republic of Germany Patent Application No.100 00 837.2-45, filed on Jan. 12, 2000, having inventors Dr. UlrichPEUCHERT and Dr. Peter BRIX, as well as their published equivalents, andother equivalents or corresponding applications, if any, incorresponding cases in the Federal Republic of Germany and elsewhere,and the references cited in any of the documents cited herein, arehereby incorporated by reference as if set forth in their entiretyherein, are hereby incorporated by reference as if set forth in theirentirety herein.

[0094] The corresponding foreign and international patent publicationapplications, namely, Federal Republic of Germany Patent Application No.100 00 836.4-45, filed on Jan. 12, 2000, [NHL-SCT-18] having inventorsDr. Ulrich PEUCHERT and Dr. Peter BRIX, as well as their publishedequivalents, and other equivalents or corresponding applications, ifany, in corresponding cases in the Federal Republic of Germany andelsewhere, and the references cited in any of the documents citedherein, are hereby incorporated by reference as if set forth in theirentirety herein, are hereby incorporated by reference as if set forth intheir entirety herein.

[0095] The corresponding foreign and international patent publicationapplications, namely, Federal Republic of Germany Patent Application No.100 00 838.0-45, filed on Jan. 12, 2000, [NHL-SCT-19] having inventorsDr. Ulrich PEUCHERT and Dr. Peter BRIX, as well as their publishedequivalents, lid other equivalents or corresponding applications, ifany, in corresponding cases in the Federal Republic of Germany andelsewhere, and the references cited in any of the documents citedherein, are hereby incorporated by reference as if set forth in theirentirety herein, are hereby incorporated by reference as if set forth intheir entirety herein.

[0096] The corresponding foreign and international patent publicationapplications, namely, Federal Republic or Germany Patent Application No.100 00 839.9-45, filed on Jan. 12, 2000, [NHL-SCT-20] having inventorsDr. Ulrich PEUCHERT and Dr. Peter BRIX, as well as their publishedequivalents, and other equivalents or corresponding applications, ifany, in corresponding cases in the Federal Republic of Germany andelsewhere, and the references cited in any of the documents citedherein, are hereby incorporated by reference as if se forth in theirentirety herein, are hereby incorporated by reference as if set forth intheir entirety herein.

[0097] The U.S. Pat. No. 5,374,595 issued on Dec. 20, 1994 to William H.Dumbaugh, Jr., et al. and entailed “High liquidus viscosity glasses forflat panel displays”, and its other equivalents or correspondingapplications, if any, and the references cited in any of the documentscited therein, are hereby incorporated by reference as if set forth intheir entirety herein.

[0098] Although only a few exemplary embodiments of this invention havebeen described in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention as defined inthe following claims. In the claims, means-plus-function clauses areintended to cover the structures described herein as performing therecited function and not only structural equivalents but also equivalentstructures.

[0099] Supplemental features which, for example, may possibly beincorporated in embodiments of the present invention may be found inU.S. Pat. No. 6,096,670 issued on Aug. 1, 2000 to Lautenschlager, et al.and entitled “Alkali metal-free aluminoborosilicate glass and its use”,U.S. Pat. No. 6,074,969 issued on Jun. 13, 2000 to Naumann, et al. andentitled “Earth-alkaline aluminoborosilicate glass for lamp bulbs”; U.S.Pat. No. 6,065,309 issued on May 23, 2000 to Cooper, et al. and entitled“Float processing of high-temperature complex silicate glasses and floatbaths used for same”; U.S. Pat. No. 6,013,310 issued on Jan. 11, 2000 toYaoi, et al. and entitled “Method for producing a thin filmsemiconductor device”; U.S. Pat. No. 6,000,241 issued on Dec. 14, 1999to Rariade, et al. and entitled “Process for making barium containingsilicate glass powders”; U.S. Pat. No. 5,985,700 issued on Nov. 16, 1999to Moore and entitled “TFT fabrication on leached glass surface”; U.S.Pat. No. 5,952,253 issued on Sep. 14, 1999 to Dejneka, et al. andentitled “Transparent apatite glass ceramics”; U.S. Pat. No. 5,932,326issued on Aug. 3, 1999 to Kashima, et al. and entitled “Ceramic wiringboards and method for their manufacture”; U.S. Pat. No. 5,908,703 issuedon Jun. 1, 1999 to Gaschler, et al. and entitled “Alkali-freealuminoborosilicate glass and its use” also referred to above; U.S. PatNo. 5,871,654 issued on Feb. 16, 1999 to Mannami, et al. and entitled“Method for producing a glass substrate for a magnetic disc”; U.S. Pat.No. 5,824,127 issued on Oct. 20, 1998 to Bange, et al. and entitled“Arsenic-free glasses”; U.S. Pat. No. 5,785,726 issued on Jul. 28, 1998to Dorfeld, et al. and entitled “Method of reducing bubbles at thevessel/glass interface in a glass manufacturing system”; U.S. Pat. No.5,770,535 issued on Jun. 23, 1998 to Brix, et al. and entitled“Alkali-free aluminoborosilicate glass and its use” also referred toabove; U.S. Pat. No. 5,707,746 issued on Jan. 13, 1998 to Yaoi, et al.and entitled “Thin film transistor device with advanced characteristicsby improved matching between a glass substrate and a silicon nitridelayer”; U.S. Pat. No. 5,374,595 issued on Dec. 20, 1994 to Dumbaugh,Jr., et al and entitled “High liquidus viscosity glasses for flat paneldisplays”, corresponding European Patent Application 0 607 865 A withdate of publication of application: Jul. 27, 1994; U.S. Pat. No.5,326,730 issued on Jul. 5, 1994 to Dumbaugh, Jr., et al. and entitled“Barium aluminosilicate glasses”; U.S. Pat. No. 5,017,434 issued on May21, 1991 to Enloe. et al. and entitled “Electronic package comprisingaluminum nitride and aluminum nitride-borosilicate glass composite”;U.S. Pat. No. 4,940,674 issued on Jul. 10, 1990 to Beall, et al. andentitled “High strength haze-free transparent glass-ceramics”; U.S. Pat.No. 4,399,015 issued on Aug. 16, 1983 to Eildo, et al. and entitled“Method for fabricating an indium tin oxide film for a transparentelectrode”; U.S. Pat. No. 4,248,615 issued on Feb. 3, 1981 to Seng, etal. and entitled “Pollution abating, energy conserving glassmanufacturing process”; U.S. Pat. No. 3,998,667 issued on Dec. 21, 1976to Rapp and entitled “Barium aluminoborosilicate glass-ceramics forsemiconductor doping”; U.S. Pat. No. 3,962,000 issued on Jun. 8, 1976 toRapp and entitled “Barium aluminoborosilicate glass-ceramics forsemiconductor doping”; U.S. Pat. No. 3,961,969 issued on Jun. 8, 1976 toRapp and entitled “Glass-ceramics for semiconductor doping”; and U.S.Pat. No. 3,907,618 issued on Sep. 23, 1975 to Rapp and entitled “Processfor doping semiconductor employing glass-ceramic dopant”.

[0100] Examples of twisted nematic and/or super twisted nematic displaysin which may possibly be incorporated embodiments of the presentinvention may be found in U.S. Pat. No. 6,023,317 issued on Feb. 8,2000to Xu, et al. and entitled “Normally white twisted nematic LCD withpositive and negative retarders”; U.S. Pat. No. 5,859,681 issued on Jan.12, 1999 to VanderPloeg, et al. and entitled “Normally white twistednematic LCD with positive uniaxial and negative biaxial retarders havingN_(x)>N_(y)>N_(z)”; U.S. Pat. No. 5,818,615 issued on Oct. 6, 1998 toAbileah, et al. and entitled “Liquid crystal display with patternedretardation films”; U.S. Pat. No. 5,694,187 issued on Dec. 2, 1997 toAbileah, et al. and entitled “LCD including negative biaxial retarder oneach side of the liquid crystal layer”; U.S. Pat. No. 5,657,140 issuedon Aug. 12, 1997 to Xu. et al. and entitled “Normally white twistednematic LCD with positive and negative retarders”; U.S. Pat. No.5,576,855 issued on Nov. 19, 1996 to Swirbel, et al. and entitled“Liquid crystal display having embossed appearing characters”; and U.S.Pat. No. 3,975,286 issued on Aug. 17, 1976 to Oh and entitled “Lowvoltage actuated field effect liquid crystals compositions and method ofsynthesis”.

[0101] Examples of active matrix liquid crystal displays (AMLCDS) inwhich may possibly be incorporated embodiments of the present inventionmay be found in U.S. Pat. No. 6,146,930 issued on Nov. 14, 2000 toKobayashi, et al. and entitled “Method of fabricating and active-matrixliquid crystal displays”; U.S. Pat. No. 6,140,990 issued on Oct. 31,2000 to Schlig and entitled “Active matrix liquid crystal displayincorporating pixel inversion with reduced drive pulse amplitudes”; U.S.Pat. No. 6,137,,558 issued on Oct. 24, 2000 to Koma, et al. and entitled“Active-matrix liquid crystal display”; U.S. Pat. No. 6,091,473 issuedon Jul. 18, 2000 to Hebiauchi and entitled “Active matrix liquid crystaldisplay”; U.S. Pat. No. 6,075,580 issued on Jun. 13, 2000 to Kouchi andentitled “Active matrix type liquid crystal display apparatus withconductive light shield element”; U.S. Pat. No. 6,052,168 issued on Apr.18, 2000 to Nishida, et al. and entitled “Active matrix liquid-crystaldisplay with verticle alignment, positive anisotropy and opposingelectrodes below pixel electrode”; U.S. Pat. No. 6,040,813 issued onMar. 21, 2000 to Takubo and entitled “Active matrix liquid crystaldisplay device and a method for driving the same”; U.S. Pat. No.6,028,578 issued on Feb. 22, 2000 to Ota, et al. and entitled “Activematrix type liquid crystal display system and driving method therefor”;U.S. Pat. No. 5,990,998 issued on Nov. 23, 1999 to Park, et al. andentitled “Active matrix liquid crystal display and related methood”;U.S. Pat. No. 5,880,794 issued on Mar. 9, 1999 to Hwang and entitled“Active matrix liquid crystal display and method with two anodizations”;U.S. Pat. No. 5,861,326 issued on Jan. 19 1999 to Yamazaki, et al. andentitled “Method for manufacturing semicoductor integrated circuit”;U.S. Pat. No. 5,808.410 issued on Sep. 15, 1998 to Pinker, et al. andentitled “Flat panel light source for liquid crystal displays”; U.S.Pat. No. 5,767,930 issued to Kobayashi, et al. and entitled“Active-matrix liquid-crystal display and fabrication method thereof”;U.S. Pat. No. 5,739,180 issued on Apr. 14, 1998 to Taylor-Smith andentitled “Flat-panel displays and methods and substrates therefor”; U.S.Pat. No. 5,650,865 issued on Jul. 22, 1997 to Smith and entitled“Holographic backlight for flat panel displays”; U.S Pat. No. Re 35,416reissued on Dec. 31, 1996 to Suzuki, et al. and entitled “Active matrixliquid crystal display device and method for production thereof”; U.S.Pat. No. 5,546,204 issued on Aug. 13, 1996 to Ellis and entitled “TFTmatrix liquid crystal device having data source lines and drain means ofetched and doped single crystal silicon”; U.S. Pat. No. 5,493,986 issuedon Feb. 27, 1996 to Augusto and entitled “Method of providingVLSI-quality crystalline semiconductor substrates”; U.S. Pat. No.5,465,052 issued on Nov. 7, 1995 to Henley and entitled “Method oftesting liquid crystal display substrates”; U.S. Pat. No. 5,184,236issued on Feb. 2, 1993 to Miyashita, et al. and entitled “Twistednematic liquid crystal display device with retardation plates havingphase axis direction with 15° of alignment direction”; U.S. Pat. No.5,182,661 issued on Jan. 26, 1993 to Ikeda, et al. and entitled “Thinfilm field effect transistor array for use in active matrix liquidcrystal display”; and U.S. Pat. No. 5,084,905 issued on Jan. 28, 1992 toSasaki, et al. and entitled “Thin film transistor panel andmanufacturing method thereof”.

[0102] Examples of thin film transistors (TFT) displays in which maypossibly be incorporated embodiments of the present invention may befound in U.S. Pat. No. 6,087,678 issued on Jul. 21, 2000 to Kim andentitled “Thin-film transistor display devices having compositeelectrodes”; U.S. Pat. No. 6,005,646 issued on Dec. 21, 1999 toNakamura, et al. and entitled “Voltage application driving method”; U.S.Pat. No. 5,920,362 issued on Jul. 6, 1999 to Lee and entitled “Method offorming thin-film transistor liquid crystal display having a siliconactive layer contacting a sidewall of a data line and a storagecapacitor electrode”; U.S. Pat. No. 5,920,083 issued on Jul. 6, 1999 toBae and entitled “Thin-film transistor display devices having coplanargate and drain lines”; U.S. Pat. No. 5,917,564 issued on Jun. 29, 1999and entitled “Methods of forming active matrix display devices withreduced susceptibility to image-sticking and devices formed thereby”;U.S. Pat. No. 5,619,357 issued on Apr. 8, 1997 to Angelopoulos, et al.and entitled “Flat panel display containing black matrix polymer”; U.S.Pat. No. 5,317,433 issued on May 31, 1994 to Miyawaki, et al. andentitled “Image display device with a transistor on one side ofinsulating layer and liquid crystal on the other side”; U.S. Pat. No.5,250,937 issued on Oct. 5, 1993 to Kikuo, et al. and entitled “Halftone liquid crystal display circuit with an A.C. voltage divider fordrivers”; U.S. Pat. No. 5,233,448 issued on Aug. 3, 1993 to Wu andentitled “Method of manufacturing a liquid crystal display panelincluding photoconductive electrostatic protection”; U.S. Pat. No.4,723,838 issued on Feb. 9, 1988 to Aoki et al. and entitled “Liquidcrystal display device”; and U.S. Pat. No. 4,404,578 issued on Sep. 13,1983 to Takafuji, et al. and entitled “Structure of thin filmtransistors”.

[0103] Examples of plasma addressed liquid crystals (PALCs) displays inwhich may possibly be incorporated embodiments of the present inventionmay be found in U.S. Pat. No. 6,094,183 issued on Jul. 25, 2000 toTanamachi, et al. and entitled “Plasma addressed liquid crystal displaydevice”; U.S. Pat. No. 6,081,245 issued on Jun. 27, 2000 to Abe andentitled “Plasma-addressed liquid-crystal display device”; U.S. Pat. No.5,997,379 issued on Dec. 7, 1999 to Kimura and entitled “Method ofmanufacturing plasma addressed liquid crystal display”; U.S. Pat. No.5,984,747 issued on Nov. 16, 1999 to Bhagavatula, et al. and entitled“Glass structures for information displays”; U.S. Pat. No. 5,886,467issued on Mar. 23, 1999 to Kimura and entitled “Plasma addressed liquidcrystal display device”; U.S. Pat. No 5,844,639 issued on Dec. 1, 1998to Togawa and entitled “Plasma addressed liquid crystal display device”;U.S. Pat. No. 5,810,634 issued on Sep. 22, 1998 to Miyazaki, et al andentitled “Method of manufacturing a plasma addressed liquid crystaldisplay device”; U.S. Pat. No. 5,757,342 issued on May 26, 1998 toHayashi and entitled “Plasma addressed liquid crystal display device”;U.S. Pat. No. 5,725,406 issued on Mar. 10, 1998 to Togawa and entitled“Plasma addressed display device”; U.S. Pat. No. 5,698,944 issued onDec. 16, 1997 to Togawa and entitled “Plasma addressed liquid crystaldisplay device”; U.S. Pat. No. 5,526,151 issued on Jun. 11, 1996 toMiyazaki, et al. and entitled “Method of manufacturing a plasmaaddressed liquid crystal display device having planarized barrier ribs”;U.S. Pat. No. 5,499,122 issued on Mar. 12, 1996 to Yano and entitled“Plasma-addressed liquid crystal display device having a transparentdielectric sheet with a porous layer containing an impregnated liquidcrystal”; U.S. Pat. No. 5,383,040 issued on Jan. 17, 1995 to Kim andentitled “Plasma addressed liquid crystal display with center substratedivided into separate sections”; U.S. Pat. No. 5,377,029 issued on Dec.27, 1994 to Lee, et al. and entitled “Plasma addressed liquid crystaldisplay”; and U.S. Pat. No.5,221,979 issued on Jun. 22, 1993 to Kim andentitled “Plasma addressed liquid crystal display and manufacturingmethod”.

[0104] The details in the patents, patent applications and publicationsmay be considered to be incorporable, at Applicants' option, into theclaims during prosecution as further limitations in the claims topatentably distinguish any amended claims from any applied prior art.

[0105] Examples of thin-film photovoltaic apparatus and methods ofmaking them in which may possibly be incorporated embodiments of thepresent invention may be found in U.S. Pat. No. 6,137,048 issued on Oct.24, 2000 to Wu, et al. and entitled “Process for fabricatingpolycrystalline semiconductor thin-film solar cells, and cells producedthereby”; U.S. Pat. No. 5,922,142 issued on Jul. 13, 1999 to Wu, et al.and entitled “Photovoltaic devices comprising cadmium stannatetransparent conducting films and method for making”; U.S. Pat. No.5,503,898 issued on Apr. 2, 1996 to Lauf and entitled “Method forproducing textured substrates for thin-film photovoltaic cells”; U.S.Pat. No. 5,378,639 issued on Jan. 3, 1995 to Sasaki, et al. and entitled“Method for manufacturing a thin-film photovoltaic conversion device”;U.S. Pat. No. 5,306,646 issued on Apr.26, 1994 to Lauf and entitled“Method for producing textured substrates for thin-film photovoltaiccells”; U.S. Pat. No. 5,057,163 issued on Oct. 15, 1991 to Barnett etal. and entitled “Deposited-silicon film solar cell”; U.S. Pat. No.4,772,564 issued on Sep. 20, 1988 to Barnett, et al. and entitled “Faulttolerant thin-film photovoltaic cell fabrication Process”; U.S. Pat. No.4,677,250 issued or Jun. 30, 1987 to Barnett, et al. and entitled “Faulttolerant thin-film photovoltaic cell”; U.S. Pat. No. 4,647,71 issued onMar. 3, 1987 to Basol, et al. and entitled “Stable front contact currentcollectors for photovoltaic devices and metod of making same”; U.S. Pat.No. 4,604,791 issued on Aug. 12, 1986 to Todorof and entitled “Methodfor producing multi-layer thin-film flexible silicon alloy photovoltaiccells”; and U.S. Pat. No. 4,595,790 issued on Jun. 17, 1986 to Basol andentitled “Method of making current collector grid and materialstherefor”.

[0106] Examples of processing technology which may possibly beincorporated in embodiments of the present invention may be found inU.S. Pat. No. 5,766,296 issued on Jun. 16, 1998 to Moreau and entitled“Furnace for melting glass and method for using glass produced therein”;U.S. Pat. No. 5,764,415 issued on Jun. 9, 1998 to Nelson, et al. andentitled “Coatings on glass”; U.S. Pat. No. 5,057,140 issued on Oct. 15,1991 to Nixon and entitled “Apparatus for melting glass batch material”;U.S. Pat. No. 5,054,355 issued on Oct. 8, 1991 to Tisse, et al. andentitled “Automatic glass cutting and positioning system”; U.S. Pat. No.4,781,742 issued on Nov. 1, 1988 to Hill, et al. and entitled “Methodand apparatus for detecting unwanted materials among cullet”; U.S. Pat.No. 4,489,870 issued on Dec. 25, 1984 to Prange, et al. and entitled“Apparatus for severing edges of a glass sheet”; and Re 30,147 reissuedon Nov. 13, 1979 to Jordan, et al. and entitled “Method of coating aglass ribbon on a liquid float bath”.

[0107] This invention as described hereinabove in the context of thepreferred embodiments is not to be taken as limited to all of theprovided details thereof, since modificatons and variations thereof maybe made without departing from the spirit and scope of the invention.

What is claimed is:
 1. An alkali-free aluminoborosilicate glass having acoefficient of thermal expansion α_(20/300) of between 2.8×10⁻⁶/K and3.8×10⁻⁶/K, which has the following composition (in % by weight, basedon oxide): SiO₂ >58-65 B₂O₃  >6-11.5 Al₂O₃ >14-25 MgO  4-8 CaO  0-8 SrO 2.6-<4 BaO  0-<0.5 with SrO + BaO  >3 ZnO  0-2


2. An alkali-free aluminoborosilicate glass having a coefficient ofthermal expansion α_(20/300) of between 2.8×10⁻⁶/K and 3.4×10⁻⁶/K, whichhas the following composition (in % by weight, based on oxide): SiO₂ >58-65 B₂O₃   >6-11.5 Al₂O₃  >14-25 MgO   4-8 CaO   0-<2 SrO >0.5-<4BaO   0-<0.5 ZnO   0-2


3. An alkali-free aluminoborosilicate glass having a coefficient ofthermal expansion α_(20/300) of between 2.8×10⁻⁶/K and 3.6×10⁻⁶/K, whichhas the following composition (in % by weight, based on oxide):SiO₂ >58-65 B₂O₃  >6-11.5 Al₂O₃ >21-25 MgO  4-8 CaO  0-8 SrO  2.6-<8 BaO 0-<0.5 with SrO + BaO  >3 ZnO  0-2.


4. The aluminoborosilicate glass according to claim 1 or 2 ,characterized in that it comprises more than 18% by weight, preferablyat least 20.5% by weight, particularly preferably at least 21% byweight, of Al₂O₃.
 5. The aluminoborosilicate glass according to at leastone of claims 1 to 4 , characterized in that the glass comprises morethan 8% by weight of B₂O₃.
 6. The aluminoborosilicate glass according toat least one of claims 1 to 5 , characterized in that it additionallycomprises: ZrO₂ 0-2 TiO₂ 0-2 with ZrO₂ + TiO₂ 0-2 As₂O₃ 0-1.5 Sb₂O₃0-1.5 SnO₂ 0-1.5 CeO₂ 0-1.5 Cl⁻ 0-1.5 F⁻ 0-1.5 SO₄ ²⁻ 0-1.5 with As₂O₃ +Sb₂O₃ + SnO₂ + CeO₂ + 0-1.5. Cl⁻ + F⁻ + SO₄ ²⁻


7. The aluminoborosilicate glass according to at least one of claims 1to 6 , characterized in that the glass is free of arsenic oxide andantimony oxide, apart from unavoidable impurities, and that it can beproduced in a float plant.
 8. The aluminoborosilicate glass according toat least one of claims 1 to 7 , which has a coefficient of thermalexpansion α_(20/300) of between 2.8×10⁻⁶/K and 3.6×10⁻⁶/K, a glasstransition temperature T_(g) of>700° C. and a density p of<2.600 g/cm³.9. Use of the aluminoborosilicate glass according to at least one ofclaims 1 to 8 as substrate glass in display technology.
 10. Use of thealuminoborosilicate glass according to at least one of claims 1 to 8 assubstrate glass in thin-film photovoltaics.